Overhead power line sensor

ABSTRACT

A power distribution monitoring system is provided that can include a number of features. The system can include a plurality of power line sensing devices configured to attach to individual conductors on a power grid distribution network. The sensing devices can be configured to measure and monitor, among other things, current values and waveforms, phase voltage, conductor current, phase-to-phase voltage, conductor temperatures, ambient temperatures, vibration, wind speed and monitoring device system diagnostics. Methods of installing and protecting the system are also discussed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. application Ser. No.15/818,512, filed Nov. 20, 2017, now U.S. Pat. No. 10,634,733, which inturn claims priority to U.S. provisional patent application Ser. No.62/424,271, filed Nov. 18, 2016, both of which are incorporated hereinby reference in their entirety.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

FIELD

The present disclosure generally relates to power distribution networks.More specifically, the present disclosure relates to integratedelectronic devices used to monitor and detect abnormalities within apower distribution network.

BACKGROUND

In providing power to customers, electrical power utility companiesemploy a power grid distribution network that includesdistribution-line-conductors (which are often referred to as powerlines). Typically, difficulties or faults within the distributionnetwork are identified only after occurrences of “events.” These eventsmay merely result in a temporary loss of power for a limited number ofcustomers, but more significant problems may occur.

Power utility companies typically employ line sensors to monitor faultson power lines. Such faults may be temporary or permanent (e.g., a blownfuse). In its usual application, the line sensor will appear passiveduring the normal operation of the power lines, and will activate whentriggered by an overcurrent exceeding a programmed threshold.

A limited number of line sensors may include rechargeable cellsharvesting solar energy and/or the electromagnetic field of theconductor to extend operational and communications availability.Harvesting energy from the electromagnetic field in the proximity of theconductor can be engineered with magnetic cores around the conductor,capturing the magnetic field created by line current flow andtransforming it to an AC voltage. Split-core toroidal transformers canbe mounted around a conductor, eliminating the need to cut and splicethe conductors.

However, current line sensors suffer from two major shortcomings: theinability to measure phase voltage on the power line and the inabilityto operate continuously with zero line current.

SUMMARY OF THE DISCLOSURE

A power line monitoring system is provided, comprising a first voltagedivider element configured to be attached to a first conductor, a secondvoltage divider element configured to be attached to a second conductor,a coiled wire connected to the first voltage divider element and thesecond voltage divider element, the coiled wire configured to adjust adistance between the first voltage divider element and the secondvoltage divider element, and a processor electrically coupled to thefirst voltage divider element and the second voltage divider element,the processor being configured to monitor a voltage of the first andsecond conductors.

It is contemplated that the first voltage divider element is attached tothe first conductor with a first clamp, and the second voltage dividerelement is attached to the second conductor with a second clamp.

The system can further include a silicon overmold configured to protectthe power line monitoring system from moisture.

The processor can be configured to continuously sample current throughthe first wire to calculate a phase-to-phase voltage.

In some examples, the system includes power harvesting electronicsconfigured to harvest energy from the first or second conductor toprovide power to the power line monitoring system.

The first and second voltage divider elements can comprise a mix ofresistive and capacitive voltage divider elements. As described herein,resistive voltage divider elements can be used by the processor tomonitor the voltage, and capacitive voltage divider elements can beconfigured to provide power to the power line monitoring system.

A power line monitoring system is also provided, comprising a firstvoltage divider element configured to be attached to a first conductor,a first rigid element connected to the first voltage divider element, asecond voltage divider element configured to be attached to a secondconductor, a second rigid element connected to the second voltagedivider element, a rigid extension element slidably disposed over thefirst and second rigid elements and configured to adjust a distancebetween the first voltage divider element and the second voltage dividerelement, a first wire connected to the first voltage divider element andthe second voltage divider element and disposed within the first rigidelement, the second rigid element, and the rigid extension element, anda processor electrically coupled to the first voltage divider elementand the second voltage divider element, the processor being configuredto monitor a voltage of the first and second conductors.

In one example of the system, the first rigid element, the second rigidelement, and the rigid extension element comprise hollow tubes. Therigid extension element can have an internal diameter larger than anexternal diameter of the first and second rigid elements.

As described herein, the first voltage divider element can be attachedto the first conductor with a first clamp, and the second voltagedivider element can be attached to the second conductor with a secondclamp.

The system can further include a silicon overmold configured to protectthe power line monitoring system from moisture.

The system can also include water drain holes disposed in the rigidextension element.

The processor can be configured to continuously sample current throughthe first wire to calculate a phase-to-phase voltage.

The system can further include power harvesting electronics configuredto harvest energy from the first or second conductor to provide power tothe power line monitoring system.

In some examples, the system further comprises a third voltage dividerelement configured to be attached to the first conductor and the firstrigid element, a fourth voltage divider element configured to beattached to the second conductor and the second rigid element, a secondwire connected to the third voltage divider element and the fourthvoltage divider element and disposed within the first rigid element, thesecond rigid element, and the rigid extension element. The first andsecond voltage divider elements can comprise resistive voltage dividerelements, and the third and fourth voltage divider elements can comprisecapacitive voltage divider elements. In some examples, the first andsecond voltage divider elements comprise a mix of resistive andcapacitive voltage divider elements.

In one implementation, the resistive voltage divider elements are usedby the processor to monitor the voltage, and wherein the capacitivevoltage divider elements are configured to provide power to the powerline monitoring system.

A power line monitoring system is also provided, comprising a firstvoltage divider assembly configured to span between a first conductorand a second conductor, a second voltage divider assembly configured tospan between the second conductor and a third conductor, firstelectronics disposed on the first conductor, second electronics disposedon the second conductor, third electronics disposed on the thirdconductor, and a wire disposed in the first and second voltage dividerassemblies and connecting the first, second, and third electronics,wherein the first, second, and third electronics are configured tosimultaneously monitor a voltage and a current on each of the first,second, and third conductors.

The first and third electronics each can comprise a current sensor, ananalog to digital converter, and a processor configured to transmitsensed data to the second electronics. The second electronics cancomprise a current sensor, analog to digital converter, at least onevoltage sensor, and a processor configured to receive sensed data fromthe first and third electronics.

The system can further include a fiber optic cable disposed in the firstand second voltage divider assemblies and connecting the first, second,and third electronics, the fiber optic cable being configured totransmit digitized sensor data from the first and third electronics tothe second electronics.

A power line monitoring device is further provided, comprising a firstconductive shell configured to substantially encircle a first conductor,a first divider equipotential surface adjacent to the first conductiveshell, a second divider equipotential surface adjacent to the firstdivider equipotential surface, the first and second dividerequipotential surfaces configured to maintain incumbent radialequipotential surfaces of the first conductor, a second conductive shellconfigured to substantially encircle a second conductor, a third dividerequipotential surface adjacent to the second conductive shell, a fourthdivider equipotential surface adjacent to the third dividerequipotential surface, the third and fourth divider equipotentialsurfaces configured to maintain incumbent radial equipotential surfacesof the second conductor, a wire connecting the first conductive shell tothe second conductive shell, and a processor configured to monitor avoltage of the first and second conductors.

The first, second, third, and fourth divider equipotential surfaces canbe semicircular in shape.

The system can further include a first rigid element connected to thefirst conductive shell, a second rigid element connected to the secondconductive shell, and a rigid extension element slidably disposed overthe first and second rigid elements so as to adjust a distance betweenthe first conductor and the second conductor, wherein the wire isdisposed within the first and second rigid elements and the rigidextension element.

The first rigid element, the second rigid element, and the rigidextension element can comprise hollow tubes. In one example, the rigidextension element has an internal diameter larger than an externaldiameter of the first and second rigid elements.

The device can further include a silicon overmold configured to protectthe power line monitoring device from moisture.

The device can further include water drain holes disposed in the rigidextension element.

The processor can be configured to continuously sample current throughthe device to calculate a phase-to-phase voltage.

The system can further comprise power harvesting electronics configuredto harvest energy from the first or second conductor to provide power tothe power line monitoring device.

In some examples, the first conductive shell is configured to place thefirst and second equipotential surfaces at known distances to the firstconductor. The second conductive shell can be configured to place thethird and fourth equipotential surfaces at known distances to the secondconductor. The first and second conductive shells are configured toallow for accurate control of the first, second, third, and fourthequipotential surface locations without regard to a diameter of thefirst or second conductors.

A power line monitoring system is provided, comprising a voltage divideradapted to be connected to a first conductor and a second conductor, thevoltage divider including a variable length electrical connectionconfigured to adjust a distance between the first conductor and thesecond conductor, the voltage divider comprising a secondary winding,and a processor electrically coupled to the voltage divider, theprocessor being configured to monitor a voltage of the first and secondconductors, wherein the voltage divider is configured to provide powerharvesting for the power line monitoring system from the first andsecond conductors while maintaining a constant voltage on the secondarywinding with a varying secondary load current on the secondary winding.

The system can further include power factor correction circuitryconfigured to appear as a resistive load on an AC source. In oneexample, the system further comprises a secondary processor on a DCoutput of the power factor correction circuitry configured to maintain aconstant current draw on a fixed DC source.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D illustrate embodiments of a power line monitoring system.

FIGS. 2A-2C show a divider conductor shell that allows control ofequipotential surface locations in the critical area immediatelyadjacent to the conductor without regard to the conductor diameter.

FIG. 3 shows power line monitors on a three-phase conductor.

FIG. 4 illustrates one embodiment of a resistive voltage divider.

FIG. 5 shows one embodiment of a capacitive voltage divider.

FIGS. 6-7 show simulated waveforms of the resistive and capacitivevoltage dividers of FIGS. 4-5.

FIGS. 8A-8F illustrate how a voltage divider influences surroundingpotential field of an electrical power grid.

DETAILED DESCRIPTION

Power line monitoring devices and systems described herein areconfigured to measure the currents and voltages of power griddistribution networks. Referring to FIG. 1A, monitoring system 100comprises monitoring device 102 mounted across adjacent power lineconductors 104 and 106 of a power distribution network. The powerdistribution network can be a three phase AC network, or alternatively,a single-phase network, for example. The power distribution network canbe any type of network, such as a 60 Hz North American network, oralternatively, a 50 Hz network such as is found in Europe and Asia, forexample. Power distribution networks, such as in the United States,typically operate at a medium voltage (e.g., 4 kV to 69 kV) to reducethe energy lost during transmission over long distances. The monitoringdevices can also be used on high voltage “transmission lines” orconductors that operate at voltages higher than 69 kV.

The monitoring device 102 can be configured to monitor, among otherthings, phase voltage, conductor current, phase-to-phase voltage,conductor temperatures, ambient temperatures, vibration, wind speed andmonitoring device system diagnostics. The monitoring devices can measurecurrent in peak amplitude or root-mean-square (RMS) values and waveformswith, for example, Rogowski coils, Hall-effect sensors, currenttransformers, or other similar current measurement devices. Phase, andphase-to-phase voltage can be similarly measured using the belowdescribed voltage divider network. Phase voltage can be measured in 4wire systems with a neutral conductor.

The monitoring device can be mounted quickly and easily via a hot-stick,and can harvest energy from the power lines for operation or beself-powered (e.g., include batteries or solar panels). The monitoringdevices can further include wireless transmission and receivingcapabilities for communication with a central server and forcommunications between each monitoring device. Installation of themonitoring device is simple, allowing the device to be placed andconfigured by a single linesman with a hot-stick and a bucket truck inless than 20 minutes. Monitoring device communication with theinstallation crew can be enabled during the installation process toprovide immediate verification of successful installation.

Referring still to FIG. 1A, the monitoring device 102 utilizes a voltagedivider 108 positioned across adjacent power line conductors 104 and106. The voltage divider 108 can include one or more voltage dividerelements 110 and 112 connected by a wire 114, which can be a singlewire, or a plurality of wires. In the simplest implementation, as shownin FIG. 1A, the voltage divider includes a single voltage divider. Inother implementations, a second voltage divider may be used to providehigher accuracy and/or higher available sensor system power as explainedbelow. The wire 114 can be straight, curved, or shaped as a spring, asshown in FIG. 1A. The voltage divider 108 can be attached to theadjacent power line conductors with a pair of clamps 116 and 118, asshown.

The monitoring device 102 further includes an electronics box 120, whichcan house the remaining electrical components of the monitoring device.For example, a current sensor, data acquisition circuitry, a powertransformer, and a WAN radio, among other features, can be containedwithin the electronics box 120. The power transformer can be used toprovide power for the operation of the monitoring device. Physically,the electronics box could be designed as an integral part of the clampand voltage divider, or it could be a separate assembly connected by therequired wire(s). An integral assembly design has the advantage of beinga simpler and possibly a more reliable design by eliminating any exposedelectrical connections. The mechanical design of the conductivecomponents in an integral assembly would be advantageously directed by3D electromagnetic field simulation software for the purpose ofmaintaining the desired E-field distribution as explained below. Aseparate assembly design has the advantage of decoupling the highvoltage design requirements of the electronics box from those of thedivider components. This could potentially provide the highestperformance solution. Another potential advantage is that it would alloworientation of the electronics box advantageously on the conductor towhich it is mounted. Note that the device will be mounted phase-to-phaseon conductor systems which can be in any arrangement, for example,horizontal, vertical, triangular, etc. Certain functions within theelectronics box may benefit from a known physical orientation, forexample, radio antennas or vibration sensors.

Referring to FIG. 1B, the electronics box can comprise sensing elements121, a power supply 123, battery 125, energy harvesting components 127including a power transformer, a microprocessor board and CPU 129, highpowered communication systems 131, including transmit and receivecapabilities, and GPS receiver 133, disposed within a robust mechanicalhousing designed for severe service conditions.

The monitoring device 102 can be configured to calculate powerparameters related to 3-phase operation, power delivery and faultconditions. Because the monitoring device 102 can, in some embodiments,have the data from all three phases, and the data or waveforms aresynchronized, calculations for 3-phase vector diagrams and 3-phase powerquality can be made.

In the illustrated monitoring device of FIG. 1A, power to operate thesensor electronics functions can be obtained from current flowing in thevoltage divider 108. A power transformer within the energy harvestingcomponents of the electronics box can be used to convert a highvoltage/low current primary winding in series with the divider to alower voltage/higher current secondary output compatible with commonpower supply electronic components. This power is available as long asthere is voltage present on the two attached conductors; distributionnetwork load current in the conductors is not necessary for operation ofthe monitoring device.

As previously mentioned, a spring design could be implemented in thevoltage divider to allow for the varying distances between conductors.The spring could be a very stiff, single turn spring, with the singleturn start-to-finish length of, for example, a foot or more. The springitself could provide the electrical connection “wire” for the voltagedivider, and/or additional wires could be wrapped with the spring. Thefull range of possible conductor movement would need to be accommodatedto prevent mechanical failure. The possible range of conductor movementcould be constrained by requiring installation reasonably close to apole.

For each installation location, there will be an ideal length (thedistance from clamp 116 to clamp 118 in FIG. 1A) for the voltagedivider. For each system voltage class, the size of the voltage dividerelements 110 and 112 in FIG. 1A will be fixed as further describedbelow. As previously mentioned, the wire 114 can be a fixed length rigidwire, or can take the form of a spring that could provide both a fixedtensile load along the voltage divider and a range of lengths withlittle tensile load variation. If a spring is used, it could be dampedto prevent mechanical oscillation. Because the resistance of the wire114 is not important, it can be any metal (e.g., bronze, stainlesssteel, etc.) and an in some embodiments, would not necessarily need tobe insulated.

FIG. 1C illustrates another embodiment in which the voltage divider 108is implemented in a rigid bar design that spans across the adjacentconductors. Referring to FIG. 1C, the monitoring device 102 comprises avoltage divider 108 incorporating a rigid hollow core tube assembly 109that includes tube elements 122 and 124 and extension tube 126. Theextension tube can have a larger internal diameter than the externaldiameter of the tube elements 122 and 124 so as to slide over the tubeelements. The length of the rigid hollow core tube assembly 109 can beadjusted by placing bolts 128 into the desired bolt holes 130, dependingon the distance between adjacent conductors 104 and 106. The voltagedivider 108, which includes the rigid hollow core tube assembly 109 andclamps 116 and 118 in FIG. 1C, can be configured to prevent undesirablephysical movement of the conductors caused by, for example, wind or ahigh current fault. In this embodiment, the device could additionally beused to provide the functionality of an existing, commonly used device,the “interphase spacer” or IPS. In this embodiment, the clamps 116 and118 can further include housings to house the voltage divider elementsand electronic components described above in FIG. 1A.

The system is designed to operate over the full spectrum of outdoorenvironmental conditions. The voltage divider (e.g., comprisingresistive and/or capacitive elements and the required electricalconnections) and the rigid hollow tube can be protected from moisture.In one embodiment, for example, the device can be protected with asilicone overmold. The bolt and hole design shown in FIG. 1C requires athrough clearance hole for the bolt in the tube element 122 and theextension tube 126. The divider network electrical connection may passthrough the inside of the tubes and would need to be protected from thebolt during installation. For highly polluted environments, a designthat swages the extension tube 126 to the tube element 122, possiblywith an additional silicone seal, may be required. This embodiment wouldnot require the bolts 128 and holes 130. If an environmental sealbetween the extension tube and the tube elements cannot be maintained,water drain holes can be placed in the extension tube.

As described above in FIGS. 1A and 1C, a single voltage divider can beused in the simplest implementation of the voltage divider 108. In thisembodiment, the voltage across and the current through the device powertransformer is continuously sampled and, using the known remainingdivider impedance, the phase-to-phase voltage is calculated.

The phase voltage measurement accuracy of a single voltage dividerdevice design will be dependent on the accuracy of the voltage dividerimpedance model. Impedance models that include significant reactance(capacitance primarily) will require one or more complex numbermultiplications at each sample time to determine phase voltage. This isof course possible, but to implement a continuously reporting voltagemeasurement system, this would have to occur in real time. This may mostrealistically be implemented in hardware, for example, a FPGA. This addsa significant level of complexity and it is anticipated that it wouldonly be used where the use of a single electrical connection through thedivider network was highly desirable.

In another embodiment shown in FIG. 1D, the monitoring device 102utilizes two voltage dividers 108 a and 108 b. Both of the voltagedividers include voltage divider elements 110 and 112 and wires 114, asdescribed above. As shown in FIG. 1D, the voltage divider 108 a is shownwith a coil or spring wire 114, while voltage divider 108 b is shownwith a straight wire 114. This is purely for illustrative purposes, toshow that either design could be used. Furthermore, the embodiment ofFIG. 1D can implement the hollow core tube design of FIG. 1C. In oneexample, both of the voltage dividers could share a single hollow coretube design. In another embodiment, each voltage divider could have itsown separate hollow core tube design between the conductors. Typicallythe same wire design would be used for both voltage dividers. In oneembodiment, the highest accuracy and bandwidth version of the dualvoltage divider monitoring device uses a dedicated resistive and/orresistive/capacitive divider for voltage measurement and a seconddivider, such as a capacitive voltage divider, as the power source forthe device. The capacitive divider can enable the highest continuousavailable system power as it minimizes heat in the divider as explainedbelow. Using a separate voltage divider network for power harvesting andvoltage measurement could also permit accurate voltage measurementduring utility network transient events that would otherwise have to beclamped to protect the device power transformer in a single dividerimplementation.

Both resistive and capacitive voltage dividers can be implemented in themonitoring device, and have benefits and drawbacks. A capacitive dividercannot obtain the voltage measurement accuracy possible in a resistivedivider design. It has the advantage however of being able to supportlarge voltage drops with little real power loss. Therefore, a capacitivedivider would be the divider of choice to provide the maximum availablecontinuous system power. In the resistive divider, voltage drops acrossthe resistive components create real power loss and therefore heat. Inthe single-circuit divider previously discussed (the “one wire”embodiment in FIG. 1A) this power loss will set the limit for thecontinuous system power available.

FIG. 1A shows two conductors 104 and 106 and could comprise the completehardware requirement for a single phase circuit. Three phase circuitscould be supported by various divider/electronics box configurations, aswill be described in more detail below. To obtain phase current andother conductor specific measurements (e.g., conductor temperature),active electronics must be present at the conductor attachment location.

Continuous system operation with several watts available will permit newdata acquisition and signal processing opportunities. For example, phasevoltage and current could be sampled at any desired bandwidth in acontinuous fashion, similar to current oscilloscope architectures, andan anomalous-event trigger algorithm could forward both current andvoltage waveforms with pre-trigger data as well as post-trigger data.

To safely enable an electrical connection between two phases of a powergrid, the existing phase-to-phase insulation system must not besignificantly compromised. This is supported in the voltage divider 108by: 1) controlling the voltage gradient through the divider and 2)providing a divider circuit insulation system.

A key feature of the device design will be its ability to maintain theperformance of the incumbent conductor-to-conductor insulation system tothe extent possible. For overhead lines, the insulation medium is air.Because the device includes a phase-to-phase electrical connection, theE-field will be disturbed by the presence of the conductive elements. Tominimize the E-field disturbance, the device can be designed with gradedimpedances between conductive elements along the length of the divideras described further below. The potential for flashover under thesecircumstances will not be controlled by divider network conductance, butby the surface conductivity of the silicone overmold used. This meansthe device's potential for flashover will be set by the siliconeovermold creep distance, hydrophobicity, and level of surface pollutioncontamination, in other words, its potential for flashover will be thesame as that for an equivalently designed IPS without an electricalconnection. This infers that the design of the device silicone overmoldinsulation system can follow that of existing field-proven IPS designs.

It is generally understood that the E-field gradient is greatestimmediately adjacent to the energized conductor and falls off veryrapidly (approximate natural log function of distance) as the radialdistance from the conductor is increased. In order to allow installationof the device in the widest range of conductor-to-conductor spacings, itis desirable to minimize the length of the divider elements 110 and 112in FIG. 1A. The shortest desirable divider element length is onedesigned to match the incumbent E-field gradients to the extentpossible. The “incumbent E-field” is the E-field that would be presentwithout a device installed. A shorter divider element length willnecessarily create higher E-field gradients through the divider elementlength, requiring an enhanced insulation system design for the device.As the divider element length is increased, E-field gradients throughthe entire length of the voltage divider 108 can be made less. The wire114 between the two divider elements 110 and 112 has a constant voltagethroughout its length, necessarily disturbing the surrounding E-field,and would create the largest incumbent E-field disturbance at the wireattachment points to the divider elements regardless of the dividerelement length used.

Equipotential surfaces can be used for all of the conductive componentsof the voltage divider element to the extent possible, again to minimizeincumbent E-field disturbance. Minimizing E-field disturbance isparticularly important for maximizing transient voltage (e.g., lightningimpulse) survival performance. If the air between two conductors cansupport the transient voltage without breakdown, then a divider systemthat does not create E-field gradients in excess of the incumbent Efield will also support the transient voltage as the divider insulatormaterial has a higher dielectric strength than air. Note that breakdowncan still occur due to insulator surface contamination. Dividers thatincorporate capacitive components require additional consideration toensure transient survival as discussed further below.

It is also understood that the E-field gradient in the vicinity of theconductor increases as the diameter of the conductor decreases. For thisreason, the device design includes a feature that creates a knownequivalent “conductor diameter”, as shown in FIGS. 2A-2C. This designallows control of the equipotential surface locations in the criticalarea immediately adjacent to the conductor without regard to theconductor diameter. This is key to controlling the accuracy of theequipotential surface voltages in close proximity to the conductor.

To minimize the current necessary through the divider for powerharvesting purposes, thereby limiting the power dissipated in any seriesresistances and limiting the value of capacitances necessary, thelargest possible voltage would be used across the power transformerprimary winding. To minimize the size, weight and cost of the powertransformer, this voltage would be advantageously limited to values thatstandard magnet wire can support. A value of 1 kV is used as an examplerealistic value.

For power harvesting purposes, it is desired that the impedance betweenthe first divider equipotential surface and the system local “ground”which is the conductor potential, be maximized. The physical distancebetween the divider conductor shell and the first divider equipotentialsurface could be quite small if it is desired to maintain a, forexample, 1 kV potential difference between the two elements. The goal inthis case would be to minimize both the area and the dielectric constantof the connecting elements as the impedance of concern will be primarilycapacitive. Physically small conductive elements are generallyundesirable for electric discharge performance, for example, corona. Aphysically small component, for example, a wire, in close proximity tothe conductor with approximately 1 kV of potential between it and theconductor is not expected to be troublesome. The primary challenge willbe the area surrounding the wire connection to the divider network, thiscan be optimized using the aforementioned 3D EM simulation software.

For voltage measurement purposes, the opposite of the above describedcase may be advantageous. A low source impedance for the voltagemeasurement divider tap may simplify or lower the cost of the associatedmeasurement electronics. The connecting “wire” in this case mayadvantageously be a flat foil or flat braided wire mounted in closeproximity to the conductor to minimize electromagnetic noise coupling tothe connection. This wire structure could also provide lower E-fieldgradients surrounding the wire, thereby minimizing corona dischargenoise coupled to the input.

FIGS. 2A-2C illustrate a divider conductor shell 232 that comprises aconductive cylindrical object that fully encircles the minimum andmaximum conductor shells 236 and 234, respectively, of a conductor 204,as shown. FIG. 2A is a cross-sectional view, FIG. 2B is a top view, andFIG. 2C is a 3D perspective view. A divider conductor shell can beplaced on each of the conductors as shown in FIG. 1C. Therefore, eachmonitoring device that spans between two conductors can include twodivider conductor shells connected by a wire 214. The wire can besurrounded by a rigid hollow tube 209 as described above. The dividerconductor shell 232 can comprise a clam shell design that can be openedand then closed over the conductor upon installation, or it can be asemicircular shape with an opening large enough to allow the maximumdiameter conductor to pass through. The conductive shells allow foraccurate control of the equipotential surface locations without regardto a diameter of the conductors, which can vary depending on theapplication.

In FIGS. 2A and 2C, two “equipotential surfaces” are shown, a firstdivider equipotential surface 238 and a second divider equipotentialsurface 240. These divider surfaces can be conductive objects whosepotentials will be designed to match the system incumbent equipotentialsurfaces as previously mentioned. The divider surfaces are showncollectively as a divider element 210 in FIG. 2B. The resistive orcapacitive element 242 shown is the impedance that provides theappropriate voltage drop through the divider. Only two equipotentialsurfaces are shown, most designs will likely use a larger number ofthese. FIG. 2C further shows an insulator 243 that encapsulates theequipotential surfaces and a portion of the wire 214. The insulatorprotects the high impedance divider network components from the weatherand supports any increased E-field gradients created by the conductiveelements of the voltage divider. In some embodiments, the insulator canbe silicon.

The resistive or capacitive element 242 in FIG. 2A can be a solidmaterial with a given resistivity to form a resistive element, or couldbe a dielectric material to form a capacitive element. Alternatively,the desired impedance could be had by using discrete resistor orcapacitor components. While one discrete component could be used, itwould likely be advantageous to use a number of components distributedthrough the available area, located, for example, at the dashed linelocations shown in FIG. 2A. This, for example, would advantageouslylower the inductance of the element for a wideband voltage measurementdivider or would spread the area available for heat dissipation in aresistive section.

The divider equipotential surface objects in FIGS. 2A and 2C are shownas semicircular. While this is a likely desirable shape, the entiredevice, including the voltage divider details would be modeled incurrently available 3D electromagnetic simulation software. This wouldenable a design that could be optimized for electromagnetic environmentperformance, voltage divider accuracy, etc.

The resistive or capacitive element 242 between the divider conductorshell 232 and the first divider equipotential surface 238 could bedesigned to support a large heat load. If the divider conductor shell232 is designed to be a substantial metallic object and it is, forexample, bolted to the conductor with a large contact surface betweenthe two, the divider conductor shell 232 would be capable of conductingconsiderable heat away from the first impedance element in the divider.Because it is possible for utility conductors to operate at elevatedtemperatures, for example 100° C. or more for brief periods, the dividercomponents (at least in the first divider section) would need to be ableto operate at these elevated temperatures. Many resistive materials anddiscrete components could be utilized at these temperatures.

As shown in FIGS. 1A-1D, two divider network assemblies will be used ateach conductor location. This provides the minimum disturbance to theincumbent E-field and is critical for safety reasons as described below.The center section of the device does not see any substantial E-fieldgradient and therefore can support a solid wire through its lengthwithout substantial detriment. This also means the extension tube 126 inFIG. 1C can be metallic without substantial detriment.

To obtain the minimum disturbance to the incumbent E-field and tomaintain a fixed range for the power transformer primary windingvoltage, a separate design would be used for each voltage class ofservice, for example, 15 kV, 25 kV, 36 kV, etc. For each voltage classof service, the actual service voltages that could be supported by thedevice would be specified. The voltage divider used for power harvestingwould be designed to source a specific range of voltage on the firstequipotential surface (and therefore the power transformer primarywinding) with a known device load current, this requires differentdivider impedances for each voltage class. To supply a constant, known,device load current requires a fixed resistive load that dissipates afixed power at the nominal power transformer secondary winding voltage.The circuitry to support this requirement is discussed further below.

A key design feature of the monitoring device is the manner of makingthe necessary electrical connections between the electronics box, theclamp, and the voltage divider. At a minimum, one electrical connectionper voltage divider network circuit used will need to be made. Thisconnection would tie to the first divider equipotential surface shownand described above in FIGS. 2A-2B.

It is anticipated that the device will be commonly installed on 3 phasedelta systems or 3 phase systems without regard to the neutralconductor. Using the device as described to this point, three deviceswould be required, each with a single electronics box attached to thealternate phases to measure the desired individual conductor parameters.Sensor data for each phase would be transmitted wirelessly via radioback to the utility SCADA system. This data could include an accuratetime stamp provided by a GPS receiver in the electronics box.

Alternatively, only two devices could be used, each device including twoelectronics boxes, one at each end. Only two of the three phase-to-phasevoltages would be measured, the third phase-to-phase voltage could becalculated from the first two.

Some considerable benefit could be had if it would be possible for oneelectronics box at an installation site to have more-or-less real timephase voltage and current data from all three phases. The voltage andcurrent data streams from the three phases would need to be timesynchronous. This would permit local calculation of important systemparameters, for example, power factor, which could be used, for example,to predict a pending utility system component failure or to indicateotherwise undetectable system disturbances and transmit them as a singleevent in near real time back the utility SCADA system. It is generallyunrealistic to stream many channels of continuous data back to the SCADAsystem and process that data from, for example, tens of thousands ofmonitors simultaneously.

To enable such a system of devices, a high speed data connection wouldhave to exist between the three sensor electronics boxes required. Thiscould be implemented via, for example, a fiber optic connection thattravels along with the divider network, a local radio connection, or anover-the-air optical connection (e.g., infrared). Time synchronizationof the data streams could be via characterization of the known hardwarepropagation delays through the system or, for example, periodiccorrection of the data stream timing could be made using an accurate GPStime stamp that is periodically transmitted along with the data.

The described system can provide time synchronized system voltage andcurrent values along with an accurate GPS-enabled real time stamp via aradio link back to a utility central processing facility. These are thekey functions of another familiar utility measurement device, the PMU(phasor measurement unit).

FIG. 3 shows a configuration that uses three electronics boxes, firstand second boxes 344 and 346 that are integrated into the clamps 316 and318 that are attached to the two outer conductor phases, conductors 304and 308, and a third, master electronics box 348, which is attached tothe center phase conductor 306. Each of the electronics boxes caninclude all of the electronics described above for electronics box 120of FIG. 1B. In some embodiments, additional electronics can be includedfor communication between each of the electronics boxes. Each of the twovoltage dividers 308 a and 308 b are constructed similar to thatdescribed in FIG. 1C. In addition to the voltage divider networkelectrical connection(s), a fiber optic cable can pass through thecenter of the rigid hollow tubes. The fiber optic cable can be used totransmit voltage, current, etc. digitized sensor data, eithermultiplexed onto a single fiber, or through multiple fiber optic linksfrom the clamp/divider/electronics boxes to the master electronics box.A cable 350 shown in FIG. 3 can connect clamps 317 and 319 to the masterelectronics box 348, including the voltage divider connection(s) and thefiber optic connections.

For ease of installation of the FIG. 3 embodiment, a single assemblycould be used. The installer would first attach, by hot stick, themaster electronics box 348 to the center conductor 306 with the twoclamp/divider subassemblies 317 and 319 dangling freely from the box bythe cable 350, fully tightening the associated clamp. The twoclamp/divider assemblies would be installed next onto the centerconductor, removing any significant slack in the cable and partiallytightening the clamps. Clamp/divider assemblies 316 and 318 would thenbe installed on the outer conductors 304 and 308, allowing the cable 350to rotate about the center conductor as necessary. As a final step, theclamps on the two center conductor clamp/divider assemblies 317 and 319would be tightened.

It is desirable for a line monitoring device to be able to runcontinuously throughout its design lifetime which could be 10 or 20years. It would be desirable for the device to continuously measure anumber of parameters, including, for example, line current, phasevoltage, conductor temperature, etc. In addition, the wireless data linkin the device can require varying amounts of power depending on thetechnology used. For example, some radios will consume 2 or 3 watts ormore during transmission. Some radio network technologies work best ifthe radio is continuously powered, for example many mesh networks.

Modern measurement data acquisition electronics can provide excellentperformance without considerable power requirements, however the presentdesign enables the inclusion in the monitor device of new measurementsand data acquisition technologies that were impractical with prior linemonitor designs. For example, it could include voltage, current,vibration, etc. measurements that ran continuously and that were storedin a FIFO buffer. These data streams could be monitored to trigger acapture of data by a local CPU based on some utility network disturbancecriteria for example. The device would be capable of returning both preand post trigger measurement data to the utility SCADA system when localCPU detects a programmed disturbance event. Higher performance CPUscould be used, running at increased clock rates. Continuous signalprocessing on the measurement data streams, for example a RMScalculation or a FFT, could be performed in hardware, for example usinga FPGA. The FPGA could be programmed through the radio link to updateits capabilities. The device could include technologies that werepreviously impractical, for example, wideband sensors for partialdischarge detection.

The above capabilities are estimated to require from 1 to perhaps 3 or 5watts. It would therefore be desirable to include in the device a powerharvesting design that could support this requirement. A transformerwhose primary winding is in series with the voltage divider networkcould be used to provide the required power. For example, a transformerwith 1000 volts across its primary winding and 1 ma of current flowingin the divider, would be capable of providing 1 watt of (lossless) poweron a secondary winding. The secondary winding could be designed tosource a convenient lower voltage that could utilize readily availableDC power supply components. The transformer design could potentiallyutilize an autotransformer winding configuration rather than a separatesecondary winding if that were advantageous, for example, for costreasons.

Both resistive and capacitive voltage dividers have been proposed. It isanticipated that a purely capacitive divider cannot obtain the voltagemeasurement accuracy or the bandwidth possible in a resistive orcombination resistive/capacitive divider design. It has the enormousadvantage however of being able to support large voltage drops withlittle real power loss. This, therefore, would be the divider of choiceto provide the maximum available continuous system power. In a resistivedivider, voltage drops across the resistive components create real powerloss and therefore heat. In a device design that utilizes a singledivider circuit that includes resistive components, this power loss willset the limit for the continuous system power available.

FIG. 4 illustrates a resistive voltage divider 408, and FIG. 5illustrates a capacitive voltage divider 508. The primary dividerelement is represented by R1 in FIG. 4 and C1 in FIG. 5. L1 and L2comprise the power transformer in each of the designs. This can be aconventional two-winding transformer, or, potentially, anautotransformer. Rload represents the proposed real power load.

Sample simulated waveforms for the resistive divider of FIG. 4 are shownin FIG. 6. For this example, a 24 kV peak conductor voltage was used,resulting in a peak current through the resistive voltage divider ofapproximately 2 ma. As seen in FIG. 6, the peak power in R1 is about 47Watts, the average (rms) power would be 23.5 Watts. This power would beshared in the two voltage divider components 110 and 112 shown in FIG.1A. The voltage across the primary of the power transformer isapproximately 1.1 kV rms. This value was chosen to represent an easilyimplemented transformer design. Higher primary voltages will yieldhigher available output powers with equal current through the divider,also decreasing the voltage necessary to drop across divider resistance.The secondary of the power transformer in this design sourcesapproximately 50V peak, 35V rms, and provides approximately 1.25 Wattsof continuous power. These values represent those that might be found inan implementation that uses a single divider circuit to provide powerand voltage measurement.

In the event that the single resistive divider design does not meeteither the continuous available power requirement or the voltagemeasurement accuracy requirement of the monitoring device, then a secondcapacitive divider can be implemented to source system power for thedevice. Simulation results for the example capacitive divider shown inFIG. 5 are shown in FIG. 7. The system parameters in this simulation arethe same as above with respect to the resistive divider, and similarvoltages are present across the primary divider element (C1). Note thatthe ideal capacitor, C1 has no real power dissipation, and therefore, noheating. This will not be zero in real capacitors, but the dissipationcould be kept as small as practically required. The available continuouspower in this example is 3 Watts peak or 1.5 Watts continuous rms.

As previously mentioned, the proposed device is designed to support aspecific utility network system voltage class. This may limit the rangeof voltage that could appear across the power transformer primary andthe transformer would be designed such that this range of voltages wouldbe supported inductively for efficient transformer operation. Thevoltage across the transformer primary will vary with the current drawnby the transformer and its load. For a single voltage divider designthat is used for both power harvesting and voltage measurement, thisideally requires a fixed resistive load, that is, a load that dissipatesa fixed power at a constant AC source voltage. This could be implementedby a number of possible circuits, for example, power factor correction(PFC) circuitry configured to appear as a resistive load on an ACsource. The DC output of the circuit would include a secondary controlsystem that maintained a constant current draw on the fixed DC source.If the device is designed with two dividers, the power harvestingdivider could operate in a much cruder fashion, that is, allow thetransformer core to saturate with light device loads. The currentthrough the divider, and the voltage on the transformer primary windingin this case would be highly nonlinear and not easily useable for phasevoltage measurement. It may also be a significant noise source that maybe difficult to attenuate.

The device will need to be able to survive the typical transient andsystem fault events seen in utility networks. These include switchingtransient events associated with either normal switching events, forexample, load transfer switching or capacitor bank switching, or theycan be sourced from a fault event, for example, recloser or circuitbreaker operation. Each voltage divider element (110 and 112 in FIG. 1A)would be preferably designed to support the full phase-to-phase systemvoltage to ensure safe operation with an exposed wire (114 in FIG. 1A)or with a wire that becomes exposed after the device becomes damaged.The device will also need to survive lightning impulse events and willbe tested to certify a specified BIL rating. These transient eventsinclude significant energy with frequency components far in excess ofnormal power frequencies (50 or 60 Hz). All of the resistive andcapacitive elements of the divider will need to be designed to dissipatethe energy associated with these events. The power transformer primarywinding will need to be protected from overvoltage and it is anticipatedthat this would be accomplished using available over-voltage protectiondevices, for example, MOVs, TVS devices, spark gaps, etc. In thisregard, a purely capacitive divider would be capable of sourcingextremely large currents, albeit for a very brief time. Divider networkseries resistance components may be desirable to limit this current inthis case. The added series resistance would favorably be distributedthroughout the length of the divider to more evenly distribute theE-field gradients created during the transient voltage fault event.

FIGS. 8A-8F illustrate a simple voltage divider design showing how atypical divider influences the surrounding potential field of anelectrical power grid. FIG. 8A shows a voltage divider 808 withcylindrical divider shells 852. The divider includes a dielectricsubstrate 854, equipotential surfaces 856, and wire 858.

FIGS. 8B-8C show top and side views, respectively, of equipotentiallines for a three conductor system having a voltage divider shells, withthe conductor sources set as follows:

Far left conductor: −1 p.u. volt

Center conductor: 2 p.u. volt

Far right conductor: −1 p.u. volt

FIGS. 8B-8C illustrate the behavior for the “incumbent field”, althoughthe diagrams include voltage divider shells on the two rightmostconductors to illustrate how they affect the field.

FIG. 8D shows the equipotential lines as they are influenced by theequipotential surfaces 856 and the wire 858 when those conductiveobjects are floating. Note the field is only changed adjacent to thecenter wire and the two connected equipotential surface elements.

FIG. 8E shows the equipotential lines for a divider design withrealistic resistances between each of the equipotential surfaces. Thefollowing resistances were used:

Between divider shell 852 and equipotential surface 856 a: 659

Between equipotential surface 856 a and equipotential surface 856 b:2880

Between equipotential surface 856 b and equipotential surface 856 c:3540

Between equipotential surface 856 c and equipotential surface 856 d:3520

Note how the potential field is most significantly influenced in thecenter area surrounding the wire 858. This is where the field is thelowest amplitude. FIG. 8F shows the same result with the dielectricsubstrate removed from the view.

The areas where the field is pinched in toward the conductor willexperience increased E-field gradients versus the incumbent field. Areaswhere the field is pinched away from the conductor experience decreasedE-field gradients versus the incumbent field. Note the areas withincreased E-field gradients surround the lower potential conductor andthe max gradient in that area will be less than the max gradientsurrounding the higher potential conductor.

As for additional details pertinent to the present invention, materialsand manufacturing techniques may be employed as within the level ofthose with skill in the relevant art. The same may hold true withrespect to method-based aspects of the invention in terms of additionalacts commonly or logically employed. Also, it is contemplated that anyoptional feature of the inventive variations described may be set forthand claimed independently, or in combination with any one or more of thefeatures described herein. Likewise, reference to a singular item,includes the possibility that there are plural of the same itemspresent. More specifically, as used herein and in the appended claims,the singular forms “a,” “and,” “said,” and “the” include pluralreferences unless the context clearly dictates otherwise. It is furthernoted that the claims may be drafted to exclude any optional element. Assuch, this statement is intended to serve as antecedent basis for use ofsuch exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Unless defined otherwise herein, all technical andscientific terms used herein have the same meaning as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. The breadth of the present invention is not to be limited bythe subject specification, but rather only by the plain meaning of theclaim terms employed.

What is claimed is:
 1. A power line monitoring system, comprising: afirst voltage divider element configured to be attached to a firstconductor; a second voltage divider element configured to be attached toa second conductor; a wire connected to the first voltage dividerelement and the second voltage divider element, the wire having avariable length to adjust a distance between the first voltage dividerelement and the second voltage divider element; and a processorelectrically coupled to the first voltage divider element and the secondvoltage divider element, the processor being configured to monitor avoltage of the first and second conductors.
 2. The system of claim 1,wherein the first voltage divider element is attached to the firstconductor with a first clamp, and wherein the second voltage dividerelement is attached to the second conductor with a second clamp.
 3. Thesystem of claim 1, further comprising a silicon overmold configured toprotect the power line monitoring system from moisture.
 4. The system ofclaim 1, wherein the processor is configured to sample current throughthe wire to calculate a phase-to-phase voltage.
 5. The system of claim1, further comprising power harvesting electronics configured to harvestenergy from the first or second conductor to provide power to the powerline monitoring system.
 6. The system of claim 1, wherein the first andsecond voltage divider elements comprise a mix of resistive andcapacitive voltage divider elements.
 7. The system of claim 6, whereinthe resistive voltage divider elements are used by the processor tomonitor the voltage, and wherein the capacitive voltage divider elementsare configured to provide power to the power line monitoring system. 8.The system of claim 1, wherein the wire is coiled.
 9. The system ofclaim 1, wherein the wire is shaped as a spring.
 10. The system of claim1, wherein the wire comprises at least a first wire and a second wire.11. The system of claim 10, wherein the processor is configured tosample current through at least the second wire to calculate aphase-to-phase voltage.
 12. The system of claim 1, wherein the wire isrigid.
 13. The system of claim 1, wherein the wire is insulated.
 14. Thesystem of claim 1, further comprising a power harvesting voltage dividerthat comprises a third voltage divider element configured to be attachedto the first conductor and a fourth voltage divider element configuredto be attached to the second conductor, wherein the third and fourthvoltage divider elements are configured to provide power to the powerline monitoring system.
 15. The system of claim 1, further comprising adivider conductor shell formed from a conductive material and configuredto be positioned around the first conductor.
 16. The system of claim 15,wherein the divider conductor shell comprises a clam shell structureconfigured to be closed over the first conductor.
 17. The system ofclaim 15, wherein the divider conductor shell has a semicircular shape.18. The power line monitoring system of claim 1, wherein the firstvoltage divider element includes one or more first equipotentialsurfaces and the second voltage divider element includes one or moresecond equipotential surfaces.
 19. The power line monitoring system ofclaim 18, further comprising a first insulator that encapsulates the oneor more first equipotential surfaces and at least a first portion of thewire; and a second insulator that encapsulates the one or more secondequipotential surfaces and at least a second portion of the wire.
 20. Apower line monitoring system, comprising: a voltage divider configuredto be attached to a first conductor and a second conductor, the voltagedivider comprising: a first conductive shell configured to be positionedaround the first conductor; a first voltage divider element configuredto be attached to the first conductor; a second conductive shellconfigured to be positioned around the second conductor; a secondvoltage divider element configured to be attached to the secondconductor; a wire connected to the first voltage divider element and thesecond voltage divider element, the wire having a variable length toadjust a distance between the first voltage divider element and thesecond voltage divider element; and a processor electrically coupled tothe first voltage divider element and the second voltage dividerelement, the processor being configured to monitor a voltage of thefirst and second conductors.
 21. The power line monitoring system ofclaim 20, wherein the first conductive shell is attached to one or morefirst equipotential surfaces and the second conductive shell is attachedto one or more second equipotential surfaces.
 22. The power linemonitoring system of claim 21, further comprising a first insulator thatencapsulates the one or more first equipotential surfaces and at least afirst portion of the wire; and a second insulator that encapsulates theone or more second equipotential surfaces and at least a second portionof the wire.